THIS INVENTION relates to reinforced concrete products.
Polymeric fibres, tapes and meshes are used as reinforcing in hydraulic matrices (also referred to as cementitous matrices). They are the conventional products of the textile and plastics industries and are primarily intended to be used for spinning and weaving, or have been produced for other purposes. The problems that hydraulic matrices, of which type 1 cement (Ordinary Portland Cement) is an example, have in interfacing with them have not hitherto been addressed to the best of Applicant""s knowledge.
The creation of polymeric reinforcing fibre, tape or mesh of high tenacity, involves a draw down or stretch ratio. This can vary in the range 5:1 to 15:1 for extruded tapes and spun multi-filaments and up to 50:1 for solvent/gel spun multi-filaments. In both cases the fibre produced has a smooth surface. Some polymers from which the fibres are made are hydrophobic. For an hydraulic matrix to achieve any significant mechanical, frictional or chemical bond to fibres or yarns made in this way is virtually impossible.
According to one aspect of the present invention there is provided yarn for use in a cement mortar matrix, the yarn including a core and a multitude of staple fibres forming a layer which envelopes the core and provides an extended surface area and interstical spaces for infiltration by cement fines and hydrates, the staple fibres being spun around the core and attached to the core, the staple fibres having sufficient freedom of radial movement to provide said spaces and permit ingress of cement fines and the formation of hydrates in said spaces.
Preferably said core comprises two or more core strands which are twisted together, portions of the staple fibres being trapped between the core strands as the core strands are twisted together thereby to form a mechanical connection between the core strands and the staple fibres. The strands of the core can have adhesive between them.
In one form said core and said staple fibres are of synthetic plastics materials which weld to one another upon being softened, the core and the fibres of the layer being welded to one another at spaced locations along the length of the yarn. In another form said fibres and said core are adhered to one another at spaced locations.
Said layer can consist mainly of fibres with hydrophobic properties intermingled with some fibres which have hydrophillic properties. It is also possible for said layer to include soluble fibres containing additives for enhancing the properties of the hydrate crystals during their formation. Alternatively the core and/or the staple fibres can have thereon a soluble coating containing additives for enhancing the properties of the hydrate crystals during their formation.